DESCRIPTION (provided by applicant: A general feature of sensory organization is that neurons can be divided into different types based on molecular, morphological, and functional characteristics. Whether this type of organization exists in the taste system is unclear. It is generally accepted that taste receptor cells exist as different types. The next critical step is to determine how these different taste receptor cell types can connect with the ganglion neurons that carry taste information to the brain. Because peripheral gustatory axons invade the tongue in fascicles, with individual axons intertwining at every level, past attempts at reconstructing single fibers have not been successful. This project will overcome this critical barrier by combining genetically-directed sparse labeling of nerve fibers with three-dimensional visualization and reconstruction in taste buds. Using these approaches, we will test the hypothesis that gustatory neurons can be divided into subtypes based on their morphology (i.e., branching) and connectivity with specific types of taste receptor cells. These experiments will reveal how connections between taste cells and nerve fibers are organized. The approaches established in this project can be used in future studies to understand 1) if morphological subtypes correspond to specific molecular and/or functional subtypes, 2) the branching of individual taste neurons in the central nervous system (CNS), 3) how branching patterns are established during development, and 4) whether normal branching patterns are reestablished following injury, disease, or chemotherapy.